This invention relates to twin tube vehicle shock absorbers which are typically mounted between the wheels and chassis or body of an automobile, for example. The invention relates to a shock absorber with damping characteristics that change depending upon the acceleration of parts of the shock absorber, most importantly, during downward acceleration of the vehicle wheel.
Shock absorbers which respond to accelerations of a vehicle wheel have demonstrated a remarkable ability to improve the performance of vehicles equipped with such shock absorbers. One such shock absorber has a movable inertia valve for opening a port during downward acceleration of the vehicle wheel . The acceleration sensitive shock absorber further includes means for biasing the inertia valve towards its open position in response to fluid flow through the shock absorber.
One type of shock absorber in current production is a monotube shock absorber with a piston dividing the inside of the tube into an upper chamber and a lower chamber. In an ordinary application, the tube is connected to the body or chassis of a vehicle and the piston is connected by way of a piston rod to the vehicle wheel. An inertia valve is mounted on the piston so that during normal operation the shock absorber is relatively stiff. Upon downward acceleration of the wheel and piston, the inertia valve opens and the shock absorber becomes softer. There are situations where it is desirable to essentially invert this relation so that the piston is connected to the body of the vehicle and the tube to a wheel. It is also desirable to employ a twin tube configuration for certain manufacturing economies. In such an embodiment, the inertia valve is desirably connected to the tubes instead of the piston so as to react upon wheel acceleration.
There is therefore provided in practice of this invention, an acceleration sensitive twin tube shock absorber having an outer tube and an inner tube with an annular reservoir therebetween. A piston movable within the inner tube divides the tube into an upper chamber and a lower chamber. An acceleration sensitive valve assembly is mounted in a base valve in the bottom of the tubes. A conduit interconnects the valve assembly and the upper chamber, and there is a rebound compliance valve for metering fluid flow from the upper chamber to the valve assembly. The valve assembly includes a port for fluid communication between the lower chamber and the conduit, and an inertial mass blocking the port in a port-closed position and not blocking the port in a port-open position. The inertial mass is normally in the port-closed position and is biased toward the port-open position upon downward acceleration of the tubes of the shock absorber. When in the port-open position, the inertial mass does not block the port, thereby permitting fluid to flow.